The gut microbiota “signature”: the key to the Mediterranean diet’s role in slowing cognitive decline

Fruits and vegetables, whole grains, legumes, nuts, and healthy fats form the foundation of the Mediterranean diet, the dietary pattern most consistently associated with overall health benefits. A large body of research has shown that following this eating pattern protects against cardiovascular and metabolic diseases, both directly—through the effects of its nutrients on the body—and indirectly, via the gut microbiota.

Now, a new study published in BMC Medicine shows that this type of diet also helps preserve cognition as we age. The research, led by scientists from Rovira i Virgili University, the Pere Virgili Health Research Institute (IISPV), both based in Tarragona (Spain), and CIBERobn (the Biomedical Research Networking Center for Obesity and Nutrition), found that adherence to the Mediterranean diet is associated with a healthier gut microbiota and slower cognitive decline in older adults with overweight or obesity and metabolic syndrome.

“People with higher adherence to the Mediterranean diet show less cognitive decline than those with lower adherence,” explains Jiaqi Ni, postdoctoral researcher at URV and first author of the study.

In a global context of population aging and rising rates of dementia such as Alzheimer’s disease, Ni adds, these findings open the door to designing dietary interventions that may help slow cognitive decline.

In this observational study, researchers followed 746 older adults over six years. All participants had overweight or obesity and were at high cardiovascular risk. The team assessed adherence to the Mediterranean diet using questionnaires, analyzed gut microbiota composition from stool samples, and monitored cognitive function throughout the study period.

“People with higher adherence to the Mediterranean diet show less cognitive decline than those with lower adherence”

According to the results, those who most closely followed this dietary pattern maintained a more diverse and favorable gut microbiota and showed better cognitive trajectories over time.

Using artificial intelligence, the researchers also identified a Mediterranean diet–specific “microbial signature.” This biomarker reflects the presence and abundance of specific gut bacteria associated with this dietary pattern.

“This ‘signature’ is based on the 20 most relevant bacterial groups linked to the Mediterranean diet, which we use to generate a score. The higher the score, the greater the adherence to the diet and the stronger the protection against cognitive decline,” says Ni. These effects may be explained by the metabolites produced by these bacteria, which have beneficial effects on overall health and support cognitive function.

“Our study shows that the microbiota is a key factor in the cognitive benefits of the Mediterranean diet,” Ni notes. “Improving diet is a simple, accessible strategy that can have real positive effects on brain health.”

Reference: Ni J, Hernández-Cacho A, Nishi SK, Babio N, et al. Mediterranean diet, gut microbiota, and cognitive decline in older adults with obesity/overweight and metabolic syndrome: a prospective cohort study. BMC Med. 2025 Dec 1. doi: 10.1186/s12916-025-04488-y.